Double ball bearing, heat treated 5 x 2" polyolefin casters (2 swivel, 2 rigid), feature 3/4" roller bearings and a hardened outer raceway for long wear and superior strength. Phenolic, Rubber on Steel and Polyurethane on Steel casters Ford 1.6L EcoBoost GTDI Engine Specs, Problems, Ford 1.6L EcoBoost GTDI Engine Review.